Liquid makeup and other viscous cosmetics are often stored in specialized cosmetics containers. In certain containers, the applicator can be affixed to the container body itself, whereby, for example, the user squeezes the container to force makeup out of the reservoir and directly into or onto the applicator.
In the case where the applicator is connected as a separate element to the container body, it is not uncommon for leakage to occur at or near the location where the makeup passes from the storage reservoir into the applicator. This leakage can occur either during use of the device, when the cap has been removed from the container, or when the device is not in use and the cap is affixed to the container. When the cap is affixed to the container, leaking makeup can accumulate under the cap, such that once the cap is removed from the container, the accumulated makeup will spill out. If the applicator is separate from the container body, there is also risk of separation.
Various types of cosmetics containers have been proposed to prevent or reduce this unintended and undesirable leakage. Certain of these containers utilized both a cap and a sealing mechanism, for example, a stopper, to prevent leakage. The sealing mechanism was designed to prevent potential leakage, and any makeup that did leak past the sealing mechanism was subsequently caught in the cap. However, a user had to perform multiple steps in order to access the makeup in these containers. For example, the user had to first remove the cap, and then disengage the stopper in order to initiate flow of makeup from the device. Multiple steps were also needed to close and store the container, in that the user had to first engage the stopper, and then place the cap on the container in order to provide maximum leakage protection when the device was not in use. Further, the sealing mechanisms were not effective to prevent leakage at the unsealed junction between the storage reservoir and the applicator, and the sealing mechanisms were often easily removable from the container (intended or unintended), which increased the likelihood of leakage.
Prior techniques for forming an elastomer applicator tip employ a co-molded elastomer and stiff support applicator tip, which is then inserted into a compression molded head of an extruded tube. This technique is time consuming and costly, and results in an unsealed junction.
See, U.S. Patent Application Ser. Nos. 60/515,680, 11/040,279, 60/570,783 (EP1595470), and 60/427,697 (WO2004/048218, U.S. Pat. Pub 2006/0137999 “[0017]A reservoir can be made by various processes, including the use of an extruded material and by injection molding. For example, a reservoir material can be formed into a cylinder (e.g., by extrusion), and sealed at one end (e.g., by heating and crimping) to form a tubular reservoir. Such a reservoir tube can be spin-welded, ultrasonic welded, or otherwise bonded to a neck, preferably before sealing. In another method, a neck/reservoir combination can be injection molded as a single piece. Preferably, when the container is injection molded, the wall thickness will be greater than when extruded components are used. Polypropylene and HDPE are preferred for injection-molded reservoirs, and all three classes of materials (polypropylene, HDPE, and co-extruded polyethylene and EVOH) are preferred for extruded reservoirs.”), expressly incorporated herein by reference.
In a co-injection molding process, a first resin is injected, and tends to form a skin against the relatively colder mold. The second resin is then injected, and fills the space within the first resin, allowing a different material on the surface than on the interior of the mold. This process is advantageous, for example, where a different color is sought at the surface, or where a higher quality material is used at the surface than in the interior. Typically, the interior material includes a portion of recycled material.
2K molding provides a flash-free, co-molded part that may eliminate the time and expense involved in additional product handling, tooling and assembly while ensuring high-quality components. In the 2K injection molding process, two molding compounds are injected into a single mold. A key factor in 2K molding is the adhesion between the different materials used. 2K molding is also known as Overmolding or insert molding, has been used with Thermoplastic Elastomers (TPEs), to result in products which have both a soft feel at the surface and strength and rigidity underneath. Rigid substrates include polypropylene (PP), polyethylene (PE), amorphous polar plastics such as polycarbonate (PC), polymethylmethacrylate (PMMA), polystyrene (PS), high impact polystyrene (HIPS), polyphenylene oxide (PPO), glycol modified polyethylene terephthalate (PETG), Acrylonitrile Butadiene Styrene (ABS), semi-crystalline polar plastics such as polyester (PET, PBT) and Polyamide (Nylon 6, Nylon 66). Many factors are very important for overmolding TPEs onto rigid substrates. The selection of the type of TPE in combination of the rigid substrate material is the first and foremost. Also important are machine type, process conditions, material preparation, part design and mold design.
Two-component injection molding has gained popularity because of its fast process time and versatility of combining a wide variety of materials. The two-component injection molding, also referred to as two-shot molding, consists of a machine with two independent injection units, each of which shoots a different material in series. The first material is injected through the primary runner system while the mold volume to be occupied by the second material is shut off from the primary runner system. The mold is then opened and the core plate is rotated and the second material is injected from the secondary runner system.
A more economical approach is insert molding. It has a lower output than two-shot molding. In insert molding, a pre-molded rigid plastic substrate or metal part is inserted into the cavity via robotics or an operator. The second (over-mold) material is either injected onto one side of the insert or sometimes completely surrounds the insert. Insert molding can be done using conventional injection molding equipment. The Overmold elastomer is usually a thin skin molded on top of the engineering substrate. Thermoplastic Elasotmers are based on hard and soft segments. These segments can either be built in the molecular architecture or created in the morphology. The hard segment determines the chemical and heat resistance of the product whereas the soft segment influences the elasticity and softness in the product.
An elastomer is a polymer having elastic properties, i.e., has the ability to readily deform under load and return to its original shape when a load is removed. Elastomers are typically amorphous polymers existing above their glass transition temperature, so that considerable segmental motion is possible. At ambient temperatures rubbers are thus relatively soft (E˜3 MPa) and deformable. Their primary uses are for seals, adhesives and molded flexible parts.
Elastomers are usually thermosets (requiring vulcanization) but may also be thermoplastic, i.e., can be remelted and hardened. The long polymer chains cross-link during curing and account for the flexible nature of the material. Example elastomers include Natural Rubber, Polyisoprene, Butyl Rubber (copolymer of isobutylene and isoprene), Polybutadiene, Styrene Butadiene Rubber or SBR (copolymer of polystyrene and polybutadiene), Synprene® (styrenic block copolymer), styrenic Nitrile Rubber (copolymer of polybutadiene and acrylonitrile, also called buna N rubbers), Chloroprene Rubber (polychloroprene, also called Neoprene), Silicone RTV (room temperature vulcanizing), LSR (liquid silicone rubber), FKM Viton®, Tecnoflon® (copolymer of vinylidene fluoride and hexafluoropropylene), Santoprene®, Fluorosilicone Rubber, EPM and EPDM rubber (ethylene propylene rubber, a copolymer of polyethylene and polypropylene), Polyurethane rubber, Resilin, Polyacrylic rubber (ABR), Epichlorohydrin rubber (ECO), Polysulfide Rubber, and Chlorosulfonated Polyethylene (CSM), (Hypalon®), for example. In general, there are classified as Styrenic block copolymers, Olefinic Copolymers, Thermoplastic Vulcanizates, Thermoplastic Urethanes, Copolyesters, and Copolyamides. Each of these chemistries offer different properties and performances related to the overmolding applications.
For the TPE to function in the application, the first and foremost requirement is to have good adhesion to the substrate and simultaneously meet other functional properties. Adhesion between the TPE and the substrate is strongly dependent on the surface energy of the two materials. Since the elastomer forms the outer surface in an overmold part there are certain ergonomic requirements for the elastomer to meet. Softness (lower durometer) is required to give cushioning and give.
Because of the inherent requirement to have good adhesion to the substrates, overmold products can have problems with mold sticking. These products usually have very low melt viscosity, which helps wetting the substrate. This helps with adhesion but increases mold wetting and if the mold is not designed will it can result in flashing. Mold sticking will result in problems with de-molding as well and can also cause the substrate to deform because of undue stresses put on the part.